The compounds possessing the following formula (II) are all known semi-synthetic cephalosporin,
such as: cefetamet (CAS registration number 65052-63-3); cefuroxime (CAS registration number 55268-75-2); cefradine (CAS registration number 38821-53-3); cefalexin (CAS registration number 15686-71-2); cefaclor (CAS registration number 53994-73-3); and cefadroxil (registration number 50370-12-2). Among them, pivaloyloxymethyl ester of cefetamet (cefetamet pivoxil, CAS registration number 65243-33-6) and 1-(acetoxyl)ethyl ester of cefuroxime (cefuroxime axetil, CAS registration number 64544-07-6) along with another above-mentioned four kinds of cephalosporin are oral antibiotics which have been used in clinic.
The compound possessing the following formula (III) is:

Sulbactam (CAS registration number 68373-14-8) halogen methyl ester, which belongs to β-lactamase inhibitor, with strong irreversible inhibition to β-lactamase released by staphylococcus aureus and many other Gram negative bacteria. It manifests extremely strong inhibition to type II, III, IV, V β-lactamase at a concentration of 2 μg/ml. If used with penicillin and cephalosporin antibiotics, it can generate synergetic effects; currently, mixed injections of ampicillin, cefoperazone, cefotaxim, ceftriaxone and sulbactam sodium salt have been used in clinic, which can prevent these antibiotics from losing antibacterial activities due to being hydrolyzed by β-lactamase, reducing minimum inhibitory concentration of these antibiotics to certain drug resistant bacteria resulting from lactamase production.
It is well known that intravenous administration is time-consuming, and has the potential threats of blood-borne infectious disease such as hepatitis B, C, AIDS etc. For those mild, moderate inflammation patients or sequential therapy of patients after intravenous anti-inflammation therapy, it is usually sufficient of oral administration, which is not only convenient and safe, but also can save a lot of manpower, material resources and wealth. However, drug resistance is quite common among oral β-lactam antibiotics to lactamase-producing bacteria, thus resulting in poor therapeutic reactions. Therefore, preparation of oral β-lactamase resistant antibiotics is actually a focus topic in the field of antibiotics manufacture.
At present, bis-esters sultamicillin (CAS registration number 76497-13-7), which is synthesized chemically by the compounds (III) and ampicillin, is an oral antimicrobial being widely used in clinic; it can be hydrolyzed to ampicillin and sulbactam by esterase of intestine walls, thus exerting the same therapeutic effects as the mixed injection of sulbactam and ampicillin. However, there is yet no compound which can chemically synthesize the compounds (III) and cephalosporin and further prepare oral β-lactamase resistant antibiotics.